Layer 4 Switching

Introduction
As networks have evolved and new technologies have emerged, multi-layer capable switches have become a popular alternative to the traditional hub, bridge or layer 2 switch. Layer 4 switching refers to an added feature and capability of Layer 3 switches. It enhances their ability to control and forward network traffic based on the information that can be derived from protocols that operate at Layer 4 of the OSI model.

Before discussing Layer 4 switches, Layer 2 and 3 capable switches should be mentioned. Traditional switches use hardware to forward network traffic at Layer 2, based on the physical MAC address of each network device. These operate very quickly and are an efficient means of handling network transmissions within LANs. Basically, it is like having a bridge, which learns, filters and forwards based on the MAC address, operate on every single port. In this way, they also reduce the amount of data that will be forwarded to the routers.

On the other hand, switches that operate at Layer 3 (similar to routers), actually calculate routes based on the logical address that is assigned by software to the data packet (such as IP addresses). Similar to routers, they have the ability to connect WANs and are more intelligent devices that can further segment network traffic to reduce congestion by calculating routes between various network links. Unlike traditional routers, which implement this technology through software and a general purpose processor that tends to have a slower data throughput, switches can perform these operations at full wire speeds. Because of increasingly advanced technology, especially in producing more advanced ICs, and especially ASICs (Application Specific Integrated Circuits), multi-layer switches are able to combine the speed and efficiency of Layer 2 switching with Layer 3 routing using a hardware implementation. This wirespeed routing technology uses hardware to perform the same functions of traditional routers, routing each packet individually, offering the advantage of being non-proprietary, and also providing the advantage of high speed communications and data throughput.

Layer 4, the Transport layer, which takes care of things like flow control and reliable and accurate delivery of the data to the next layer, uses protocols such as TCP and UDP. These protocols include the port number information in the header, which helps identify what application the packet is being used by or is intended for. This information can be very useful in handling network traffic because many well known applications use designated ports. For example, port 80 is generally used by HTTP, and ports 20 and 21 by FTP. Because a Layer 4 switch can identify this information, together with the IP address that is identified on Layer 3, it not only knows where the data needs to go, but also what application will use it. The combination of a Layer 4 TCP or UDP port number and the Layer 3 address is called a socket.

This information can be used to enhance the features of a Layer 3 switch, which essentially performs packet routing at high speeds by means of hardware, by allowing it to filter network traffic and perform switching based on the application the data is intended for. So, a Layer 4 switch has the ability to not only examine the IP address, but also to control the traffic based on the port numbers located at Layer 4 of the OSI model.

Packet Filtering and Prioritization
This gives Layer 4 switches the ability to implement a variety of services that take advantage of this application specific information. For example, routers are often used as a network firewall, filtering packets and providing security features by either allowing or blocking certain connections. A Layer 4 switch can offer this same service, but implement it by means of hardware, thus offering the same service with a much higher speed of data throughput.

Layer 4 switches can also use this information to prioritize traffic flow. Because it can see both the port number and IP address of a data packet, it can give priority to data intended for mission critical applications. For example, data intended for the HTTP (port 80) application on a web server can be given higher priority than data intended for another application that may be running on that same server. This provides that application a higher class of service. This can be used to ensure QoS (Quality of Service), which basically refers to a guaranteed throughput level.

Load Balancing
Another service that can be made possible by a Layer 4 switch is load balancing. Load balancing can be implemented to more efficiently control the amount of information that a particular server, among a group of servers supporting the same application, may receive.

For example, a group of physical servers that are being used as a web server farm can all be grouped together into one virtual, or logical, server. The new virtual server, made up of these physical servers, would be assigned just one IP address. Traffic intended for these servers would be directed towards this IP address. A Layer 4 switch can then manage load balancing among the group that makes up the virtual server. The data can be balanced among the servers based on a number of factors. For instance, by keeping track of how many sessions each individual server is supporting, traffic can be forwarded to the server with the least number of sessions. Or, traffic can be distributed based on a percentage. The faster servers can be assigned a higher percentage, and the slower servers can be assigned a smaller percentage of the overall network traffic. These are just a couple of ways this load balancing can be implemented. But in any case, this provides a more efficient means of handling traffic on the network by avoiding overloading any one physical server.

The way that I was able to visualize how this works and make sense of this load balancing feature was by thinking about how traffic lights at a major intersection are programmed and timed. Since the major roadway handles the majority of the traffic, the traffic light for that path is set to have a larger portion of time to allow for the traffic to flow. Then, the side streets that pour into that road are given a smaller percentage of time, based on how much traffic they produce. Of course, this method of balancing the timing of the lights based on traffic needs makes more sense than giving each light an equal amount of time. And so to me, this is why it makes sense for a network to make use of load balancing as well.

Conclusion
Based on this research, Layer 4 switching technology greatly enhances the intelligence of the network. It allows the switch to make specific, intelligent decisions based on the information it derives from both Layers 3 and 4 so that it can handle this data in the most efficient way. One of the greatest benefits of a Layer 4 switch is that this intelligent decision making capability is implemented by means of high speed hardware, thus allowing todays high capacity networks to function very efficiently.
...courtesy www.comtest.com

Cisco Password Recovery

Introduction
This document describes the procedure for recovering an enable password or enable secret passwords. These passwords are used to protect access to privileged EXEC and configuration modes. The enable password password can be recovered but the enable secret password is encrypted and can only be replaced with a new password using the procedure below.

Note: This password recovery procedure works for the following Cisco products:

Cisco 806
Cisco 827
Cisco uBR900
Cisco 1003
Cisco 1004
Cisco 1005
Cisco 1400
Cisco 1600
Cisco 1700
Cisco 2600
Cisco 3600
Cisco 4500
Cisco 4700
Cisco AS5x00
Cisco 6x00
Cisco 7000 (RSP7000)
Cisco 7100
Cisco 7200
Cisco 7500
Cisco uBR7100
Cisco uBR7200
Cisco uBR10000
Cisco 12000
Cisco LS1010
Catalyst 2948G-L3
Catalyst 4840G
Catalyst 4908G-L3
Catalyst 5500 (RSM)
Catalyst 8510-CSR
Catalyst 8510-MSR
Catalyst 8540-CSR
Catalyst 8540-MSR
Cisco MC3810
Cisco NI-2
Cisco VG200 Analog Gateway
Route Processor Module


Step-by-Step Procedure
Attach a terminal or PC with terminal emulation to the console port of the router. Use the following terminal settings:
9600 baud rate
No parity
8 data bits
1 stop bit

If you still have access to the router, type show version and record the setting of the configuration register; it is usually 0x2102 or 0x102.

If you don't have access to the router (because of a lost login or tacacs password), you can safely consider that your configuration register is set to 0x2102.

Using the power switch, turn off the router and then turn it back on.
Important: To simulate step 4 on a Cisco 6400, pull out and then replace the Node Route Processor (NRP) or Node Switch Processor (NSP) card.
Important: To simulate step 4 on a Cisco 6x00 using NI-2, pull out and then replace the NI-2 card.

Press Break on the terminal keyboard within 60 seconds of the power-up to put the router into ROMMON.
If the break sequence doesn't work, see Possible Key Combinations for Break Sequence During Password Recovery for other key combinations.

Type confreg 0x2142 at the rommon 1> prompt to boot from Flash without loading the configuration.

Type reset at the rommon 2> prompt.
The router reboots but ignores its saved configuration.
Type no after each setup question or press Ctrl-C to skip the initial setup procedure.

Type enable at the Router> prompt.
You'll be in enable mode and see the Router# prompt.
Important: Type configure memory or copy startup-config running-config to copy the nonvolatile RAM (NVRAM) into memory.

Type write terminal or show running-config.
The show running-config and write terminal commands show the configuration of the router. In this configuration you see under all the interfaces the shutdown command, which means all interfaces are currently shutdown. Also, you can see the passwords (enable password, enable secret, vty, console passwords, and so on) either in encrypted or unencrypted format. The unencrypted passwords can be re-used, the encrypted ones will have to be changed with a new one.

Type configure terminal and make the changes.
The prompt is now hostname(config)#.
Type enable secret to change the enable secret password, for example.

Issue the no shutdown command on every interface that is used. If you issue a show ip interface brief command, every interface that you want to use should be "up up".

Type config-register 0x2102, or the value you recorded in step 2.

Press Ctrl-z or end to leave the configuration mode.The prompt is now hostname#.
Type write memory or copy running-config startup-config to commit the changes.
Example of Password Recovery Procedure
The example below presents an actual password recovery procedure. We created this example using a Cisco 2600. Even if you are not using a Cisco 2600, this example will be almost exactly what you experience on your product.

Router>enable
Password:
Password:
Password:
% Bad secrets

Router>show version
Cisco Internetwork Operating System Software
IOS (tm) C2600 Software (C2600-IS-M), Version 12.0(7)T, RELEASE SOFTWARE (fc2)
Copyright (c) 1986-1999 by cisco Systems, Inc.
Compiled Tue 07-Dec-99 02:21 by phanguye
Image text-base: 0x80008088, data-base: 0x80C524F8

ROM: System Bootstrap, Version 11.3(2)XA4, RELEASE SOFTWARE (fc1)

Router uptime is 3 minutes
System returned to ROM by abort at PC 0x802D0B60
System image file is "flash:c2600-is-mz.120-7.T"

cisco 2611 (MPC860) processor (revision 0x202) with 26624K/6144K bytes of memory.
Processor board ID JAB031202NK (3878188963)
M860 processor: part number 0, mask 49
Bridging software.
X.25 software, Version 3.0.0.
Basic Rate ISDN software, Version 1.1.
2 Ethernet/IEEE 802.3 interface(s)
2 Serial(sync/async) network interface(s)
1 ISDN Basic Rate interface(s)
32K bytes of non-volatile configuration memory.
8192K bytes of processor board System flash partition 1 (Read/Write)
8192K bytes of processor board System flash partition 2 (Read/Write)
Configuration register is 0x2102
Router>
!--- The router was just powercycled and during bootup a
!--- break sequence was sent to the router.
!

*** System received an abort due to Break Key ***

signal= 0x3, code= 0x500, context= 0x813ac158
PC = 0x802d0b60, Vector = 0x500, SP = 0x80006030
rommon 1 > confreg 0x2142

You must reset or power cycle for new config to take effect

rommon 2 > reset

System Bootstrap, Version 11.3(2)XA4, RELEASE SOFTWARE (fc1)
Copyright (c) 1999 by cisco Systems, Inc.
TAC:Home:SW:IOS:Specials for info
C2600 platform with 32768 Kbytes of main memory


program load complete, entry point: 0x80008000, size: 0x6fdb4c

Self decompressing the image : ###############################
##############################################################
##############################################################
##############################################################
############################### [OK]


Restricted Rights Legend

Use, duplication, or disclosure by the Government is
subject to restrictions as set forth in subparagraph
(c) of the Commercial Computer Software - Restricted
Rights clause at FAR sec. 52.227-19 and subparagraph
(c) (1) (ii) of the Rights in Technical Data and Computer
Software clause at DFARS sec. 252.227-7013.

cisco Systems, Inc.
170 West Tasman Drive
San Jose, California 95134-1706

Cisco Internetwork Operating System Software
IOS (tm) C2600 Software (C2600-IS-M), Version 12.0(7)T, RELEASE SOFTWARE (fc2)
Copyright (c) 1986-1999 by cisco Systems, Inc.
Compiled Tue 07-Dec-99 02:21 by phanguye
Image text-base: 0x80008088, data-base: 0x80C524F8

cisco 2611 (MPC860) processor (revision 0x202) with 26624K/6144K bytes of memory.
Processor board ID JAB031202NK (3878188963)
M860 processor: part number 0, mask 49
Bridging software.
X.25 software, Version 3.0.0.
Basic Rate ISDN software, Version 1.1.
2 Ethernet/IEEE 802.3 interface(s)
2 Serial(sync/async) network interface(s)
1 ISDN Basic Rate interface(s)
32K bytes of non-volatile configuration memory.
8192K bytes of processor board System flash partition 1 (Read/Write)
8192K bytes of processor board System flash partition 2 (Read/Write)


--- System Configuration Dialog ---

Would you like to enter the initial configuration dialog? [yes/no]: n

Press RETURN to get started!

Router>

Router>enable
Router#copy startup-config running-config
Destination filename [running-config]?
1324 bytes copied in 2.35 secs (662 bytes/sec)
Router#
00:01:24: %LINEPROTO-5-UPDOWN: Line protocol on Interface BRI0/0:1, changed state to down
00:01:24: %LINEPROTO-5-UPDOWN: Line protocol on Interface BRI0/0:2, changed state to down
Router#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#enable secret cisco
Router(config)#^Z
00:01:54: %SYS-5-CONFIG_I: Configured from console by console

Router#show ip interface brief
Interface IP-Address OK? Method Status Protocol
Ethernet0/0 10.200.40.37 YES TFTP administratively down down
Serial0/0 unassigned YES TFTP administratively down down
BRI0/0 193.251.121.157 YES unset administratively down down
BRI0/0:1 unassigned YES unset administratively down down
BRI0/0:2 unassigned YES unset administratively down down
Ethernet0/1 unassigned YES TFTP administratively down down
Serial0/1 unassigned YES TFTP administratively down down
Loopback0 193.251.121.157 YES TFTP up up
Router#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#interface Ethernet0/0
Router(config-if)#no shutdown
Router(config-if)#
00:02:14: %LINK-3-UPDOWN: Interface Ethernet0/0, changed state to up
00:02:15: %LINEPROTO-5-UPDOWN: Line protocol on Interface Ethernet0/0, changed state to up
Router(config-if)#interface BRI0/0
Router(config-if)#no shutdown
Router(config-if)#
00:02:26: %LINK-3-UPDOWN: Interface BRI0/0:1, changed state to down
00:02:26: %LINK-3-UPDOWN: Interface BRI0/0:2, changed state to down
00:02:26: %LINK-3-UPDOWN: Interface BRI0/0, changed state to up
00:02:115964116991: %ISDN-6-LAYER2UP: Layer 2 for Interface BR0/0, TEI 68 changed to up
Router(config-if)#^Z
Router#
00:02:35: %SYS-5-CONFIG_I: Configured from console by console

Router#copy running-config startup-config
Destination filename [startup-config]?
Building configuration...
[OK]

Router#show version
Cisco Internetwork Operating System Software
IOS (tm) C2600 Software (C2600-IS-M), Version 12.0(7)T, RELEASE SOFTWARE (fc2)
--- output truncated ---
2 Ethernet/IEEE 802.3 interface(s)
2 Serial(sync/async) network interface(s)
1 ISDN Basic Rate interface(s)
32K bytes of non-volatile configuration memory.
8192K bytes of processor board System flash partition 1 (Read/Write)
8192K bytes of processor board System flash partition 2 (Read/Write)
Configuration register is 0x2142

Router#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#config-register 0x2102
Router(config)#^Z
00:03:20: %SYS-5-CONFIG_I: Configured from console by console

Router#show version
Cisco Internetwork Operating System Software
IOS (tm) C2600 Software (C2600-IS-M), Version 12.0(7)T, RELEASE SOFTWARE (fc2)
--- output truncated ---
2 Ethernet/IEEE 802.3 interface(s)
2 Serial(sync/async) network interface(s)
1 ISDN Basic Rate interface(s)
32K bytes of non-volatile configuration memory.
8192K bytes of processor board System flash partition 1 (Read/Write)
8192K bytes of processor board System flash partition 2 (Read/Write)

Configuration register is 0x2142 (will be 0x2102 at next reload)
Router#

The Internet

The Internet is a standardized, global system of interconnected computer networks that connects millions of people. The system uses the Internet Protocol Suite (TCP/IP) standard rules for data representation, signaling, authentication and error detection. It is a network of networks that consists of millions of private and public, academic, business, and government networks of local to global scope that are linked by copper wires, fiber-optic cables, wireless connections, and other technologies. The Internet carries a vast array of information resources and services, most notably the inter-linked hypertextdocuments of the World Wide Web (WWW) and the infrastructure to support electronic mail, in addition to popular services such as video on demand, online shopping, online gaming, exchange of information from one-to-many or many-to-many byonline chat, online social networking, online publishing, file transfer, file sharing and Voice over Internet Protocol (VoIP) orteleconferencing, telepresence person-to-person communication via voice and video.

The origins of the Internet reach back to the 1960s when the United States funded research projects of its military agencies to build robust, fault-tolerant and distributed computer networks. This research and a period of civilian funding of a new U.S. backbone by the National Science Foundation spawned worldwide participation in the development of new networking technologies and led to the commercialization of an international network in the mid 1990s, and resulted in the following popularization of countless applications in virtually every aspect of modern human life. As of 2009, an estimated quarter of Earth's population uses the services of the Internet.(Courtesy Wikipedia)